Bounded linear maps #
This file defines a class stating that a map between normed vector spaces is (bi)linear and
continuous.
Instead of asking for continuity, the definition takes the equivalent condition (because the space
is normed) that ‖f x‖
is bounded by a multiple of ‖x‖
. Hence the "bounded" in the name refers to
‖f x‖/‖x‖
rather than ‖f x‖
itself.
Main definitions #
IsBoundedLinearMap
: Class stating that a mapf : E → F
is linear and has‖f x‖
bounded by a multiple of‖x‖
.IsBoundedBilinearMap
: Class stating that a mapf : E × F → G
is bilinear and continuous, but through the simpler to provide statement that‖f (x, y)‖
is bounded by a multiple of‖x‖ * ‖y‖
IsBoundedBilinearMap.linearDeriv
: Derivative of a continuous bilinear map as a linear map.IsBoundedBilinearMap.deriv
: Derivative of a continuous bilinear map as a continuous linear map. The proof that it is indeed the derivative isIsBoundedBilinearMap.hasFDerivAt
inAnalysis.Calculus.FDeriv
.
Main theorems #
IsBoundedBilinearMap.continuous
: A bounded bilinear map is continuous.ContinuousLinearEquiv.isOpen
: The continuous linear equivalences are an open subset of the set of continuous linear maps between a pair of Banach spaces. Placed in this file because its proof usesIsBoundedBilinearMap.continuous
.
Notes #
The main use of this file is IsBoundedBilinearMap
. The file Analysis.NormedSpace.Multilinear
already expounds the theory of multilinear maps, but the 2
-variables case is sufficiently simpler
to currently deserve its own treatment.
IsBoundedLinearMap
is effectively an unbundled version of ContinuousLinearMap
(defined
in Topology.Algebra.Module.Basic
, theory over normed spaces developed in
Analysis.NormedSpace.OperatorNorm
), albeit the name disparity. A bundled
ContinuousLinearMap
is to be preferred over an IsBoundedLinearMap
hypothesis. Historical
artifact, really.
A function f
satisfies IsBoundedLinearMap 𝕜 f
if it is linear and satisfies the
inequality ‖f x‖ ≤ M * ‖x‖
for some positive constant M
.
Instances For
A continuous linear map satisfies IsBoundedLinearMap
Construct a linear map from a function f
satisfying IsBoundedLinearMap 𝕜 f
.
Equations
- IsBoundedLinearMap.toLinearMap f h = IsLinearMap.mk' f (_ : IsLinearMap 𝕜 f)
Instances For
Construct a continuous linear map from IsBoundedLinearMap
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Taking the cartesian product of two continuous multilinear maps is a bounded linear operation.
Given a fixed continuous linear map g
, associating to a continuous multilinear map f
the
continuous multilinear map f (g m₁, ..., g mₙ)
is a bounded linear operation.
We prove some computation rules for continuous (semi-)bilinear maps in their first argument.
If f
is a continuous bilinear map, to use the corresponding rules for the second argument, use
(f _).map_add
and similar.
We have to assume that F
and G
are normed spaces in this section, to use
ContinuousLinearMap.toNormedAddCommGroup
, but we don't need to assume this for the first
argument of f
.
A map f : E × F → G
satisfies IsBoundedBilinearMap 𝕜 f
if it is bilinear and
continuous.
Instances For
A bounded bilinear map f : E × F → G
defines a continuous linear map
f : E →L[𝕜] F →L[𝕜] G
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Useful to use together with Continuous.comp₂
.
Useful to use together with Continuous.comp₂
.
The function ContinuousLinearMap.smulRight
, associating to a continuous linear map
f : E → 𝕜
and a scalar c : F
the tensor product f ⊗ c
as a continuous linear map from E
to
F
, is a bounded bilinear map.
The composition of a continuous linear map with a continuous multilinear map is a bounded bilinear operation.
Definition of the derivative of a bilinear map f
, given at a point p
by
q ↦ f(p.1, q.2) + f(q.1, p.2)
as in the standard formula for the derivative of a product.
We define this function here as a linear map E × F →ₗ[𝕜] G
, then IsBoundedBilinearMap.deriv
strengthens it to a continuous linear map E × F →L[𝕜] G
.
Equations
Instances For
The derivative of a bounded bilinear map at a point p : E × F
, as a continuous linear map
from E × F
to G
. The statement that this is indeed the derivative of f
is
IsBoundedBilinearMap.hasFDerivAt
in Analysis.Calculus.FDeriv
.
Equations
Instances For
The function ContinuousLinearMap.mulLeftRight : 𝕜' × 𝕜' → (𝕜' →L[𝕜] 𝕜')
is a bounded
bilinear map.
Given a bounded bilinear map f
, the map associating to a point p
the derivative of f
at
p
is itself a bounded linear map.
The set of continuous linear equivalences between two Banach spaces is open #
In this section we establish that the set of continuous linear equivalences between two Banach spaces is an open subset of the space of linear maps between them.